you really need 6cf minimum for those 3 subs the port at 35Hz ( too low in my Professional opinion for an L7 ) would be a slot port 14.5 tall by 5 wide and 17 deep which gives you 12" per cube of port area. In over 15 years selling Kicker I have never heard 1 sound good with a round port, or in less than 2 cubes per 10 and 2.5 for the 12's. 38Hz is where they get the loudest and still sound the best they can. if you keep the 5.24 gross cf you have now and tune at 38 you may increase output but you dont have near enough power either. for 38 with what you have a slot port would be 14.5 x 4.5 x 14.25 deep. it is the best option IMO without rebuilding a new box which is what i would do at 7cf gross. and at least 1800 rms